refinement vs improvement

refinement and improvement both are nouns.

Word	Noun	Adjective	Verb	Adverb
refinement	Yes	No	No	No
improvement	Yes	No	No	No

As nouns, improvement is a hypernym of refinement; that is, improvement is a word with a broader meaning than refinement:

Other hypernyms of refinement include advance, betterment.

refinement (noun)	improvement (noun)
the quality of excellence in thought and manners and taste	the act of improving something
a subtle difference in meaning or opinion or attitude	a change for the better; progress in development
the result of improving something	a condition superior to an earlier condition
the process of removing impurities (as from oil or metals or sugar etc.)
a highly developed state of perfection; having a flawless or impeccable quality